Holiday flyers take note: The federal Transportation Security Administration (TSA) has been quietly removing its admittedly cancer-causing full-body X-ray scanners known as “backscatter” machines from seven large US airports. About 280 are still in use at about 40 airports.

Public opposition and criticism from health scientists, the ACLU and Congress have pressured the TSA to either get rid of the machines or make them less invasive. The X-ray systems are being replaced with “millimeter-wave” technology — machines that use radio waves similar to cell phones — at Los Angeles International, Chicago O’Hare, Orlando, Logan International in Boston, and Kennedy and LaGuardia in New York City.

Jay Stanley with the American Civil Liberties Union told the Associated Press that the scanners “continue to be surrounded by health questions.” The ACLU’s gripe with the machines is that the X-ray images of passengers’ naked bodies are an invasive assault on privacy. The millimeter wave machines produce a stock image with software that alerts the TSA to any potential weapons or explosives.

Other critics raised health questions, especially regarding children, infants, fetuses and pregnant women, all of whom are more vulnerable to radiation than the “”Reference Man” used often to quantify radiation risk. In December 2010, routine maintenance of the machines showed they were emitting more than 10 times the radiation expected. The TSA said then that the results were due to a mathematical error and that all the machines are safe.

Michael Grabell in the October Mother Jones reports, as I noted last year in these pages, that prominent scientists have accused the TSA of “unnecessarily endangering the public” because of the availability of the alternative (and even cheaper) millimeter wave technology.

“Why would we want to put ourselves in this uncertain situation where potentially we’re going to have some cancer cases?” David Brenner, the director of Columbia University’s Center for Radiological Research said to ProPublica last year.

Prominent Scientists Raising Alarms

Scientists at the Univ. of California, San Francisco and Arizona State Univ. have raised profound questions — as yet unanswered by TSA or Rapiscan, the machines’ manufacturers — about the health effects of backscatter scanners which bounce X-rays off travelers’ bodies.

Dr. John Sedat, an emeritus professor in biochemistry and biophysics at UCSF co-signed a letter to the White House last year that criticized the veracity of safety tests done on the machines. He charged that “the risk of radiation emission to children and adolescents does not appear to have been fully evaluated.” Sedat’s letter also raised alarming concerns about pregnant women and fetuses.

The TSA did not say the change was the start of a complete phase-out of the scanners and is currently moving the contraptions to smaller US airports. As the safety of millimeter-wave systems has not been established, cautious passengers may still want to opt for the old fashioned “pat down.”

One year ago, the European Union took the advice of Brenner and Sedat and banned the use of X-ray body scanners in European airports. The EU opted for the precautionary ban on the X-ray machines, “In order not to risk jeopardizing citizens’ health and safety.”

The case of the backscatter X-ray machines being removed from Orlando, Florida is interesting, and recalls the adage about the squeaky wheel. The Orlando Sun reported last January that Broward County officials had repeatedly raised health and safety questions about the X-ray machines. The county wrote letters to the TSA asking its opinion of the European Union ban, and Broward Aviation Director Kent George also asked if TSA had conducted “recent studies” on the scanner and “its effects on the health/safety of the frequent traveler.”

The TSA did not say the limited changes were the start of a complete phase-out of the scanners, and it is currently moving the contraptions to smaller US airports. We can watch for them at say Duluth and Minneapolis.

As the safety of millimeter-wave scanners has not been well-established, cautious passengers, especially women, children and infants, may still want to opt for the old fashioned “pat down.”

John LaForge is a co-director of Nukewatch and edits its Quarterly newsletter.